Nylon 6, a polymer of caprolactum, is a well-recognized engineering plastic. As is characteristic of these materials, nylon is strong, it is capable of withstanding considerable abuse, it has low coefficient of friction, long wear life and makes an excellent bearing element.
U.S. Pat. No. 4,001,124 discloses the use of minor amounts of polyolefin and polyfluorocarbon fillers to increase the wear life of a plastic bearing material. In a preferred embodiment the polyolefin is an ultra-high molecular weight polyethylene (UHMWPE), the polyfluorocarbon is polytetrafluoroethylene (PTFE) and the plastic matrix is nylon.
The present invention improves on the formulation of U.S. Pat. No. 4,001,124 in that it provides a further increase in the wear life of nylon 6.
Measurement of Wear Life
For the purposes of this specification, examples and claims, the wear life of a bearing is measured as the K wear factor.
The test procedure used to determine the K wear factor is a common one in the plastic bearing art. A 1/2 inch diameter journal bearing is machined from a sample and a steel shaft is inserted into the bearing for rotation. The shaft is rotated under loads measured in pounds per square inch, at velocities measured in feet per minute and the wear depth of the journal bearing is measured in inches after 200 hours. K is then calculated by substituting the recorded values in the following equation: EQU K=h/PVT
in which h is the wear in inches, P is the pressure in psi, V is the velocity in ft./min., and T is the time in hours. This results in a K number having units of in..sup.3 min./ft.lb.hr. and, for convenience, is expressed in values of 10.sup.-10. A low K indicates long wear and a high K indicates poor wear resistance.